The present invention relates to a paging channel selection system in a mobile communication system.
The conventional control flow in a mobile station is shown in FIG. 2. The idea of FIG. 2 is shown in the JP patent laid open publication 64-51832 dated Feb. 28, 1989.
FIG. 3 shows a model of a mobile communication, in which the numerals 1, 2 and 3 are paging control zones, and 4 is a mobile station.
In a mobile communication system, a P-channel (paging channel), an S-channel (speech channel), and an A-channel (access channel) are provided between a mobile station and a base station. A P-channel is used for establishing a connection when a call is originated in a network, or a mobile station receives a call. An A-channel is used for establishing connection when a call is originated in a mobile station. When the connection is established, the channel is switched from a P-channel or an A-channel to an S-channel for speech. A mobile station is in a waiting state when no communication is carried out, and receives a P-channel which is broadcast by a base station.
Each base station has specific paging channel (P-ch), and a plurality of speech channels. In FIG. 3, a first zone which is specific to a first base station has a paging channel P1, and ten speech channels S11-S20, a second zone has a paging channel P2 and ten speech channels S21-S30, and a third zone has a paging channel P3, and ten speech channels S31-S40.
When a power switch is put on (10) in a mobile station, the mobile station selects one of the paging channels (P-CH) which are stored in the mobile station so that the selected paging channel has the receive level higher than a predetermined level, and the reception of broadcast information is possible in waiting state (12). When a mobile station stays in the first zone 1, the paging channel P1 which is specific to the zone 1 will be selected. When the paging channel is selected, the mobile station goes into the waiting state (14). The mobile station monitors the receive level of the selected channel (P-ch). When the receive level in that channel is decreased because of the movement of the mobile station to another paging zone, the selection of another paging channel is effected as is the case when the power switch is put on.
During the waiting state, assuming that an originating call or a terminate call occurs, the channel is switched to an S-channel (speech channel), and the communication is effected in that speech channel. When the communication finishes, the channel is switched again to the paging channel (P-CH), and the operation state is changed to the waiting state.
When the mobile station stays in the first paging zone, and does not move to another paging zone during the speech (case a in FIG. 3), there is no problem, and the mobile station operates in the waiting state in the paging channel P1 after speech end.
However, when the mobile station moves to another paging zone (case b in FIG. 3) during the speech, the paging channel which the mobile station takes at the end of the speech is the first paging channel (P1) which was taken at the beginning of the speech. Therefore, it is much possible that the receive level of the paging channel (P1) at the end of the speech is lower than the predetermined level, and the search of the new paging channel (P2) must be effected as is the case when the power switch is put on. Therefore, it takes some time to go to the waiting state after the end of the speech. The new call is impossible from the end of the previous speech to the establishment of the waiting state, and the service quality is decreased by the above problem.
The above problem is serious when the size of paging zones is small as compared with the moving length of a mobile station.